modify a vhf uhf antenna diamond x50

[Ur5by9]

I have a diamond x50 which is no longer in use and would like to modify it to work slightly out of its band.

Opening it up there is not a lot inside however What id like to understand Is that can the lengths be adjusted to alter either the 145mhz or 432mhz portions of this antenna.

The antenna is split up with coils , could it be possible to adjust the uhf 70cm to be resonant on 446 whilst retaining the 145 or would any adjustments in the lengths affect both bands this is designed to work from.

Ideally it would be nice to have the 145 side working on the air band and the 432 section on the 446.

Picture bellow taken from another website of the internals and sizes.

[Alan Pilot]

Don't see why you can't tune the top section for the pmr.

[paulears]

Don’t forget that part of the performance of these comes from the fact that the uhf section is bolstered by the vhf section resonating at 3 times the frequency as a ¾ wave, so 446 is actually pretty near that area. Interesting things might happen?

[deadite66]

interested to know what swr you have for yours, mine is under 2.0 at 446MHz.

[Ur5by9]

I am going to need an antenna analyser for the uhf which i dont currently own.
I think ch25 recommended the nano vna which sould help me get a better idea.

Not fully understanding how the duel band antenna functions I am learning a bit along the way.
But I start to understand when paulears said that its 3x 3/4 wave which is 435mhz or there about if you work that from 145mhz

Maybe if the antenna could be made more broadband over a wider range would be a good trade off.

Its our hobby and we like to tinker with things i guess.

[paulears]

I've been selling a variation of the D30 dual bander for a few years now and have experimented a bit. Sticking them on the analyser doesn't produce anything remotely like I actually imaged before I bought the analyser and tracking generator. I assumed that the response would gradually increase then decrease as we approached 145MHz and the same with UHF but clearly the individual separate components stacked together interact, so you get odd notches and peaks. I believed that the antenna was actually a VHF section with a UHF on top. However, tweaking the UHF section had a small effect at the VHF end, and adjusting the VHF very clearly changed the coupling with the UHF. I've just ordered a selection of different VHF and UHF antennas from new manufacturers (to me) because while my office is quite low, being in a harbour, my home is on a hill top - not a huge hill, but higher than many areas around here. I've got a UHF repeater at home, and while it usually runs single antenna, I have another antenna I could use for twin antenna working. I have a very elderly Jaybeam single band commercial antenna that has 4.5dBd gain, and the other antenna is a commercial J-pole, which claims 2dBd gain, but has a 60 degree beam width - and the two seem quite close in what they seem to do. I've not put the analyser on these two - which would be interesting. Maybe I'll bring it home and try it and see what the performance looks like?